In silicon microactuators, one means of converting electrostatic energy into work is to dispose structures “as a comb”, formed respectively by moveable and fixed fingers and set at two different potentials. The moveable fingers are attached to the combs, themselves attached to a nacelle guided linearly by springs. These actuators are produced by photolithography and dry plasma attack of monocrystalline silicon layers having a thickness typically of 50 to more than 200 microns.
In order to make a clock wheel turn, it is necessary to convert the linear movement into rotational movement, via a ratchet system for example, as in the case of Accutron watches by Bulova (USA), Mosaba by ETA or via a hysteresis system such as described in the document WO 2004/081695. The linear movement on silicon being of the order of a few tens of microns, the ratchet driven by the pawls must have teeth of equivalent dimensions. In order to ensure reliable meshing, the positioning of this ratchet relative to the moveable fingers must by within tolerances which are much lower than the some tens of microns mentioned earlier.
In order to produce such a mechanical interfacing between the linear movement of a pawl actuator and the rotational movement, the document WO 2006/024651 proposes using microactuators which drive, by means of a tooth in a hysteresis movement, a micromanufactured wheel with very small teeth, which is coaxial and integral with a clock pinion. This solution implies an adjustment of the microactuators relative to the wheel for each assembled piece because the radial positioning tolerance of one mechanism axle, for example a plain bearing made of steel on ruby, is of the order of 40 microns. One solution can be to integrate a spring system on the MEMS in order to take up the positioning clearance, such as a bending mechanism of the ratchets, which is proposed in the document WO 2006/97516. The positioning is therefore ensured but the pawls or any other mechanism made of silicon therefore protrude directly on the side of the chip which makes manipulation during assembly more difficult and also its exposure to dust more direct.
The invention aims to resolve these problems by proposing an arrangement in which the microactuator drives a silicon rotor positioned on the same substrate as the microactuator. The invention aims to make the micromotor and the mechanism independent at the level of their radial clearances (radial play), whilst allowing transmission of the pure torque from one to the other.